Today I took this for its 1st test drive, and it works well...
I have the Pi 4 in a Ugreen Car Phone Dashboard Holder connected to a Samsung Galaxy S21 on one of the Pi USB3 ports. The Pi is getting power from the car cigarette socket using a Ugreen 24W Car Charger. The S21 is also connected to the Parrot over Bluetooth.
The only thing I changed from my last post was I disabled the speech and music channels in the CrankShaft Audio channels under settings. This allows my phone to send the audio towards the Parrot which is wired into the original car radio.
( CrankShaft Wiki )